a. Field of the Invention
The present invention relates to a temperature measurement system for free turbine type gas turbine engines and more particularly, but not exclusively, for gas turbine engines of relatively low forward speed applications.
B. Description of Prior Art
In order to maintain gas turbine engine operation within safe limits and to ensure adequate life of the hot components, it is required to monitor or control the turbine inlet temperature. Current means of indirectly determining turbine inlet temperature involve the measurement of temperature at three locations, namely, engine inlet, compressor delivery and engine exhaust. This arrangement, where the temperature at the turbine inlet is obtained by simple addition and/or subtraction of the three temperature measurements, is applicable only to turbojet engines where virtually all the output of the turbine is consumed within the engine. For turboprop or turboshaft engines, where a substantial amount of energy is used for external work, some allowance must be made to the temperature in the exhaust area. The configuration of some gas turbine engines is such that sensing turbine inlet temperature is impractical or very difficult, particularly for maintenance reasons because of inaccessability of the temperature probes and harness in this area. Also, the heat at the turbine inlet area is too severe for good thermocouple life. In a free turbine engine, the measurement of the turbine inlet area temperature is also not so easily obtained because of power variations possible at the free turbine in relation to the fixed compressor turbine.